Cold front in July!

My forecast for temps over the next 4 days

A bona fide cold front is moving southward through the United States today, and will move all the way through most of Alabama, Mississippi, Tennessee, and Georgia tomorrow!

The term “cold front” is always used to describe the front edge of cool air masses that replace warmer ones. Of course, it is not going to get “cold” here in the Southeast U.S., but it will certainly feel much more pleasant than the sauna we have felt the past 3 weeks, with morning lows dropping near 60 degrees as far south as Birmingham and Atlanta, and daytime high temperatures only in the mid 80s.

Current temperatures (1 pm CDT)

The above map shows current temperatures from SE Kansas to NW Alabama right now. Some of the lower temperatures over parts of KY and AR are being affected by rain. But, it is 79 in Joplin, MO at 1 pm, and they have sunshine! So, this is a legitimate cool air mass. By tomorrow afternoon, winds will turn out of the north along I-20 from Jackson to Birmingham to Atlanta, and the cooler air will be moving in.

The air in places like Birmingham and Nashville will be coming from the eastern Great Lakes, as the NOAA computer model trajectories show below.

We will see some rain showers and maybe a few thunderstorms as the front moves through overnight and tomorrow morning. But, from tomorrow afternoon through Thursday, temperatures will be below normal. Some locations in the colder valleys of northeast AL, north Georgia, and east TN will easily drop well into the 50s.

Another big change that will make it feel nice will be the much lower humidity. Dewpoint is a meteorologist’s favorite measure of water vapor in the atmosphere because it is not affected by temperature, it simply indicates how much water vapor is in the air. The dewpoints over much of the Southeast U.S. the past few weeks have been between around 73, indicating a water vapor content of 17.5 grams of water vapor for every kg of air. Tuesday through Friday, dewpoints will be in the 50s, indicating water vapor contents dropping by 50%, to about 9 grams per kg. You will feel the difference!

Enjoy it, because with the strong, nearly overhead sunshine angle of July and August and warm soil, it won’t last, and we should be back into the 90s by the weekend. The humidity will come back too, with a big Gulf of Mexico nearby and water temperatures in the 80s.

Dr. Tim Coleman

Twitter @timbhm

http://www.colemanandknupp.com

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